Heating up food, in particular milk, to an acceptable temperature is an essential part of the nutrition cycle for infants. This can either be breast milk that is stored in the fridge or formula milk that is prepared from tap water or cooled down boiled water. An acceptable temperature for the milk is for most infants between 30 and 40-42° C. and more preferably between 35 and 39° C. Research shows that if the milk temperature is over 40° C. for more than 20 minutes, then the essential nutrition parts such as proteins and vitamins will be damaged.
There are several different methods of heating-up milk or food. These can be microwave heating, steam heating and water bath heating (also known as au bain-marie heating). Microwave heating method has the disadvantage that heating is not uniform in the milk and locally the milk can become very hot, causing nutrition damage. With steam heating steam is condensing on the bottle wall. It has however a disadvantage that the milk temperature inside the milk can be non-homogeneous, also resulting in parts (at the top of the bottle) of the milk that can become too hot. This is also noticed by consumers.
The au bain-marie principle is heating of milk by placing the milk in a container, in particular a baby bottle, in liquid, in particular water, which is heated via a heating element at the bottom of a chamber. This is the most common technology being used in many heating devices. One of the essential advantages of an au bain-marie system is that the heating of the milk occurs relatively uniform, i.e. there is only a small temperature gradient in the milk.
Currently, the user has to roughly define by trial and error the heating time of the baby bottle in the chamber in order to achieve the desired milk temperature. When the baby bottle is not taken out in the right time interval the milk will continue to heat up. As there is a tremendous variation in baby bottle types, sizes, milk and water volume, baby bottle wall thickness and initial milk and water temperature it is not possible for a manufacturer to give accurate advice in the manual on how long the baby bottle should be heated to achieve the required temperature.
An essential problem for a bottle warmer is that the milk temperature inside the bottle is not known. It appears rather difficult to measure the milk temperature directly in the bottle. There are bottles with temperature indicators, however these are relatively inaccurate. Further it is very difficult to read these temperature indicators when the milk is in the bottle warmer. Bottle warmers known in the past employ complex algorithms to estimate the milk temperature, wherein the algorithms are not able to be implemented in a simple micro-controller of average bottle warmers. Additionally, not all the assumptions are held in the real use case scenarios due to the uncontrolled parameters and noises.
U.S. Pat. No. 6,417,498 B1 discloses a receptacle-type heating device for automatically warming and vibrating a multitude of containers simultaneously in order to thaw, warm, and mix cold or frozen liquid. The device heats each container to a desired temperature using heat exchange of heated water with the container. A heater of the device comprises a thermostat device to set the device to a desired stable temperature.
WO2007/022507A2 discloses a method and an apparatus capable of determining the amount of time remaining before a food being heated reaches a desired temperature and/or a food reaches approximately room temperature by directly measuring the temperature of the food. Determining the amount of time remaining is based at least on the rate of temperature change of the food during heating/cooling.